Recent years have seen tremendous growth in the number and variety of display devices available to the public. Computers (whether desktop, laptop, or notebook), personal digital assistants (PDAs), mobile phones, and thin LCD TVs are but a few examples. Although some of these devices can use ordinary ambient light to view the display, most include a backlight to make the display visible.
Many such backlights fall into the categories of “edge lit” or “direct lit”. These categories differ in the placement of the light sources relative to the output face of the backlight, where the output face defines the viewable area of the display device. In edge lit backlights, a light source is disposed along an outer border of the backlight construction, outside the area or zone corresponding to the output face. The light source typically emits light into a light guide, which has length and width dimensions on the order of the output face and from which light is extracted to illuminate the output face. In direct lit backlights, an array of light sources is disposed directly behind the output face, and a diffuser is placed in front of the light sources to provide a more uniform light output. Some direct lit backlights also incorporate an edge-mounted light source, and are thus capable of both direct lit and edge lit operation.